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TSR Wiki > Study Help > Subjects and Revision > Revision Notes > Chemistry > Chemistry Higher Topic - Elements and Bonding

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Chemistry super summary topic 1

Contents 1 Metal lattice 2 Monatomic elements 3 Molecular elements 4 Covalent network elements 5 Atomic size 6 Ionisation energy 7 Periodic table 8 Comments

Metal lattice

Pattern of delocalised electrons surrounding a pattern of fixed cores.

Metal atoms have fixed centre and free electrons (delocalised) makes them good conductors as electrons that can flow.

Malleability- rolled into sheets -----\ depends on free moving bonding

Ductile- stretched out -----/

Down a group= decreasing boiling point

Across periods= increase in boiling point

Monatomic elements

Exist as single atoms in gas state

Weak electrostatic attractions called van der Waal's between temporary dipoles

Constantly moving electron cloud induces dipoles, delta + or -, delta means ‘slightly’

It is the only bonding between monatomic elements.

It gets stronger the bigger the atom is.

Molecular elements

Covalent bond- electrostatic attraction between shared electrons and +ive nuclei of 2 atoms

Diatomic- iodine, bromine, chlorine, fluorine, oxygen, nitrogen and hydrogen

Number of atoms in molecule increases and therefore strength of van der Waals forces between molecules increase

Fullerenes- 60 carbon atoms. Low density, highish BP due to van der Waal's

Covalent network elements

Carbon (diamond), boron and silicon.

Solids at room temp, high MP/BP

Graphite- 1st set of electrons hold atoms in sheets covalently, 2nd set of electrons are delocalised, conduct along the sheets

Layers can slide, good solid lubricant, tends to be used in the desert where oils couldn't be used (freezes in the cold desert, is hindered by sand in the hot desert)

Atomic size

Covalent radius (distance between to covalently bonded nuclei halved)

Van der Waals radius- distance between 2 radius of van der Waals bonding halved)

Along period, size decreases due to increased nuclear attraction + density increases

Down a group, atom size increases due to added electron shells + density decreases

Ionisation energy

Energy required to remove one electron from every atom in one mole of free atoms, measured in kJ mol^-1. Ion formed is always positive.

Values in data book

Across period ionisation energy increases due to increased nuclear attraction

Down a group - ionisation energy decreases due to shielding layers of electrons

2nd ionisation energy – energy required to remove a second electron from every ion in a mole of ions.

Periodic table

Invented by Mendeleev, made a ‘periodic law’ and then put it in a table

He left some spaces as he predicted more elements would be discovered.

Comments